Oscillograph.



J. T. DBMPST'ER.

OSGILLOGRAPH.

APPLICATION FILED FEB,14,1908.

Patented Apr. 20, 1909.

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v fNx/:ENTUR JUHN 177 L' PETER.

MTNESSE'E.' Wm L Sm. i5;. f- @zw J. T/DBMPSTERQ OSGILLOGRAPH. APFLIOATIOH. FILED H1B. 14,1908.

Patented Apr. 20, 1909 z sHBBTs-sHB2T z.

.NVENTH JDHN ZY DEZ/[PETER E Y l QM c UNITED s'mrusrernur ortica JointI Trios. recuperen, or sounnuofrnnr, New Yorin, .essienon To GENERAL concluir, a conroai'rioiv. or New Your.

ELECTRIC osonnnccnern.

Speccaticn of Letters Patent.

Patented pmi 2 0, 1999.

Application led February le, 1908. Serial No. 415,850.

To ,all'fwho'm "Lt may conce-mr.

Be 1t known tltat I, JOHN' T. DEMPSTER, e

subject of'the'King of Great Britain, residing,r at Schenectady, in the county of Schenec tady, State of New York, have .invented certain new and useful lm rovements in Oscillographs, of which the ollowing'is a spccii cation.

My invention relates to oscillograpbs and similar instruments for investigatin' conditions on electric circuits, its object being to simplify and im rove the construction of these devices an( iarticularly to provide e simple and rugged ilevice by means of which a current or voltage curve may be projected on a screen o rother receiving surface on any desired scale.

The standard oscillograph heretofore used consists essentially of a reflecting galvanometerin which the mirror oscillates about ,a vertical axisin response to changes in volte-ge or current on the circuit to which the instrument is connected, and a beam of' flight reflected from the mirror moves to and fro in a straight horizontal line over a screen or similar receiving surface. lf it is desired to trace out a curve of current or voltage', the beam of light from the galvanometer mirror must be reilected to the screen from a second 'mirror oscillated about ari-airis at right angles to the axis of the galvanometer mirror and in synchronism with the alternations of-current or voltage on the circuit v connected to. the galvanometer. The curve lsecured from the standard instrument above described is on a small scale and cannot be vprojected on a screen before an audience with satisfactory results, andthe whole apparatus must be inclosed in a lightetight box when it is used in daylight or in a-lighted room.

ln carrying out my. invention I provide a galvanometer with a movable member, preferably a mirror, mounted so that it can r move in one direction in response to variations in voltage or current in the circuit to which it is connected, and .also in\another direction, preferably-at rightangles to the iii-st, in synchronis'm.` with the periodic changes in current or voltage on that circuit. As a result of the simultaneous movement of the mirror in two directions at right an,- gleeA to eacifotber, the beam of light reflect,- ed from the mirror will trace out uponthe screen a curveaccurately representing` tire the instrument is connected, and. the scaley upon which the curvo is traced is determined by the distance of the screen fromv the instrument. The moving member or mirror of the ali-'anomcter may be mounted in many dliiercnt ways to secure two movements at an angle tov cach other, one desir able way being to mount the member to move about two axes at right angles to each other, the movement about one axis varying with either the voita'e or current in the circuit to which the gaciyanonieter is connected, while the movement about the other axis is in synchronism with that circuit. l'n

the preferred lconstruction the mirror, con

nected so as to swing or vibrate in response to current o r voltage, is mounted on a, support which 1s pivoted between the poles of a magnet and is vibrated about its pivots by means of some device, s uch as el chronous motor, which will give 1t a motion having a definite time relation to the vibrations of the mirror, which vibrates at a rate dependent on the frequency of the circuit to which the instrument is connected. l

My invention will best be understood in connection with the accompanying drawin s,

which are merely illustrative of some of t emany forms in which the invention may be embodied, and in which- Fivure 1 is a plan View of an instrument embodying my invention; Fig. 2 an end View of tlifainstrument shown in Fig. l on a. section along the. line a b; Fig,` 3, a Vdetail side View of the support for the movable element of the alvanoi'neter; Fig. 4 is'another view of the evice shown in Fig. 3; Fig, 5 an end view ofj a synchronous motor showingone form of a. starting device; Fig. 6 an end view of a modified formv of instrument shown with parts broken away; and Fig. 7 a view looking down upon the instrument shown in Fig. 6', with parts broken away.

The particular form of instrument shown in Fig. l is mounted'upon a suitable base l,

with pedestals 2 for supporting a magnet 3,

which supplies an intense magnetic field for a reflecting galvanometer in which the mirror or similar movable reecting member ,is mounted to move in two-directions at right angles to each other. lThe mirror 7 moves in one direction, orvibrates about a vertical because it cemented t0 e 'looped ductor 5 connected to the circuit and mainsupport l by means of a spring 8.

and forth in a tained under tension across bridges 6 on the The mirror 7 is movable in another direction at right angles to the first because the support 4 is movable at right angles to the axis of movement of the mirror, which is cemented to the conductor between the bridges. The su port 4 also carries wedge-shaped iron. o e pieces J with their inner ends on eachsl c cf and parallel to the conductor 5 near the mirror, and the other ends in close sliding engagement with the poles 10 of the n1agnet3,so that the pole pieces are part of the magnetic circuit of the magnet, although movable with relation to it. 'lne support 4 carrying the pole pieces 9 maT be movably mounted in any suitable way, and is shown mounted upon ivots 11 'carried by the magnet 3, so that tlie support can oscillate about a horizontal axis extending through the pole pieces of the magnet, and since the axis of vibration of the mirror is vertical, the two axes are. at right angles to each other and intersect in the plane ofthe mirror, which is movable about either axis. The pole pieces 9 are in good contact with the poles 10 of the'magnet,`and conduct the magnetic ilux with very little loss, so that an intense )rimary field is maintained around the con uctor in spite of the tact that the )ole pieces 9 move with reference to the poles 10 of the magnet. Current is sus lied to the looped conductor 5 through lexi lialeads 12 connected to terminals 13 on the base, and sets up around. the looped con ductor a secondary field which varies With the new of current and causes the looped conductor to vibrate about a longitudinal axis in accordance With changes in current, thereby causing the mirror to turn to an extent I ependent on the strength of the current, the beam of light from the mirror swinging back horizontal line as the current in the conductor varies.

The arrangement described constitutes a galvanometer which is exceedingly sensitive, and in which the vibrations of the mirror 7 about an axis parallel to the conductor vary in amplitude with veryslight variations in the current through thev conductor. The beam of light from the mirror will trace. out upon a screen a curve representing the periodic vibrations of the mirror about its vertical axis, if the sup port 41's rocked in any suitable Inanner about its horizontal axis in some definite time relation to the periodic vibrations of the mirror about its vertical axis. The preferred arrangement for rocking the support in delinite time relation to the mirror is shown in the drawings, in which a two-pole synchronous motor7 comprising ield magnets 14 and an armature 15, is provided with any suitable starting device, such as that shown at 16 comprising a' brush which may be brought into engagement with the armature during the period of starting. This synchronous moi l l lution of `the shaft 17 causes one complete vibration or oscillation of the support 4 and the rate of vibration of the support depends upon the frequency of the alternating current circuit to which the motor is connected.

The instrument above descr'bed Will cause a beam. of light reflected from the mirror 7 to trace out a curve on the screen,but in order to avoid confusion it is necessary to pret'fentv an indication 'appearing on the screen during the time ing from its extreme position to its initial position, as otherwise the sine curve of an alternating circuitv would screen inthe form of a accomplish this result the reflection of the beam oi' light from the mirror to the screen during a deiinite part of each Vibration of the support 4 prevented by any suitable device, such as a shutter 22 mounted on the shaft 17 and proportioned to cut othe light from the mirror during nearly a half revolution of the shaft, during which time the support 4 returns to its initial position, whereupon the shutter moves awa from in front the support is returnfigure 8. In order to appear on the retrace the curve. Y This invention may be embodied in galvanometers in which the moving elementis constructed in different` ways, and in the modification shown in Fig. 6 the magnet 3 is provided with fixed pole-pieces 23 'suitably shaped and tapered to produce an intense magnetic held between their tips. An iron strip 24 carrying a small mirror 24*1 is strung under tension between the pole tips so as to be subject to the ported in'a movable frame. 25 mounted to vibrate or oscillate about pivots 26 on the pole pieces of the magnet-3. The frame 25 is .oscilla-ted indefinite. time relation to the periodic swings of the mirror 24 by means of the earn 18 in the same manner as the support 4 of the instrument shown inl Fig. 1 is oscillated. The iron strip with the small mirror is caused to oseillate about a vertical axis in response to variations of voltage or current by means of two current coils 27 mounted on each side of the pole pieces of the magnet 3 and energized by current flerived from the circuit ou'which the instrunient is used, while the supporting frame is oscillated b f the synchronous motor about a horizonte axis intersecting the axis of the strip in the plane of the mirror.

The operation of the instrument shown'in Fig: 1 is as follows: The terminals 13 and the synchronous motor are connected to the circuit under investigation in such a manner that @urteilt derivedfrom the circuit and rn synchrenism Awith either the voltage or lcurrent 'df the circuit flows through the conductor 5, causing the mirror to vibrate about sits 'vertical Aaxis iny response to the ciirrentV through'the galvanometer and in s'rnchrowith the circuit, While the sync ronous motor, whichjhas been brought up to speed byn'ieans of the starting device 16, vibrates iunrroscillatesthe supv rt 4 about its `horihentai axis at a rate ependent upon the freqnencfy ofthe circuit, and in definite time `relation to the mirrors periodic swings or vibrations, which alsb depend upon the frequency of the circuit. A beam of light dlrooted on the mirror 7 is' reilected back on anysuitable screen and traces out upon the 'screen a curve, of which one dimension varies with .the angular osition of the support 4,

While the other. i'mension varies with the -amount of current through the conductor 5. As the support 4 makes a complete movement in one direction from its initial position f the mirror swings through a complete cycleand 'a-shar-ply defined curve represen-ting .the

complete cycle is.l traced out uporthe screen'.

The shutter 22, by. cutting oif the beam of iight ifrom' the mirror, prevents any indicar'- vtien 'on the`\scr een during the movement of the :support back toits 'initial positi'cnfand thereby'prevents the curve appearing in the form ofya loop -or figure '8. As soon as the supporta reaches its initial position the shut- -t'cr22 moves from in front ofthe mirror, and ,35 th'cfbeaml of lightretraces the curve, which', owing `to the persistence of vision, appears stead-y and does not flicker if the 'frequency @of the circuit is 25 cycles or greater. The curve may be projected on a screen before 4o an audience upon a scale so large that the curve may be easily seen and studied by every member. of the audience, since the -scale depends upon the distance of the screen from theinstrument, While the curvev may be made sharp .and easily visible by throwing a very intense light on the mirror. e

The operation of the `forms shown in Figs. 6 and 7 1's the same as that ab`ove described, the onlyl difference being that the mirror 24a. mounted on the iron strip swings about its vertical axis in response to current through the current coils 27.

While the principal field of service of the instrument is in taking curves of current or electromotivaforce it may, by means which will be readily understood by engineers, be used -to take watt curves or any curves of a periodically varying force. y

My invention may be embodied in many otherforms than that shown and described, and l, therefore, do not wish to be restricted to thc exact form shown, but intend to cover.

by the appended claims all changes and modifications Within the spirit and scope 'of my invention.

What I claim as new and desire to secure bjyLetters iatent of the United States, ism

.v 1. In an oscillograph, the combination 'With a galvanometer comprising a magnet for producing a primary magnetic iield, a vibratory member which produces a secondary magnetic iicld and is mounted in said primary -iield to vibrate about two axes" perpendicular to each other, and connections whereby the mutual'eiiect of said primary and said secondary fields is varied in response to variations of current through 'the galvanometer to cause said member to vibrate about one axis, of means for vibrating said member about the other axis at a rate Awhich bears a definite relation to its rate of vibration about the rst axis. v

2; ln an oscillograp'h, the combination with a galvanometer comprising a magnetic field, a'current carrying conductor mounted in the field of said magnet to vibrate about two .axes perpendicular' to eachA other and connections for supplying current to said conductor to Acause 'it to vibrate about one I,axis in response to variations in current through the galvanometer, of means for viv`.bratingsaid member about its other axis at a'iiate which bears. a definite relation to its 'rate of vibration about the -iirst axis.

3. In au oscillograph, the "combination with a galvanometer comprising a magnet for producing a primary magnetic field, a support pivoted adjacent said magnet to vibrate about its pivot, a current caxryingconductor mounted on said support to extend into said iield and to vibrate about a longiv -tudinal axisperpendicular to the pivot cf said support, and connections for supplying currentto said conductor to cause it to vibrate about Aits longitudinal axis in.response to variations in current through the galva l nometer, of means'for vibrating said support about its pivot at a rate which bears a-denite relation to the rate of vibration of said conductor about its longitudinal axis.

, 4. ln -anv oscillograph, the combination with a galvanometer comprising a magnet for producing a magnetic field, a support pivoted adjacent said field, a looped current carrying' conductor strung on said'support to4 bring both sides of said conductor into said field and to'leave said conductor free to vibrate about a longitudinal axis perpendicular to the pivot of said support, a mirror secured to said conductor, and connections for supplying current to said conductor to cause 1t to vibrate about its 'longitudinal axis '1n response to variations in current through the galvanometer, of means for vibrating sald support aboutits pivot in synchronism With the current throughjhe conductor.

.5. In an oscillograph, the combination with a galvanometer comprising a el magnet, a member mounted between the poles oi said magnet to vibrate about two intersect-4 port, and moons for vihrutingr suiii support in s),'nr,hronisn1 with sniil current.

7. in :in ost'illogruph, the eomhinution with n field magnet, oi' n sop ,ort mounted to vibrate about :1n axis extenring throughv the poles of snifl mrgnet pole pieces euri-imi on saiil support in Contact with shirt poles, z. ,movable member mounted on seid support to vibrate between said poie pieces shout un exis intersecting the axis oi' vibration ot snirl support, and Ineens for vibrating seid support in synehronism with sniil member.

8. ln an osciliogrnph, the combination with o field magnet, of n support mounted to move bet-Ween the poles ol said magnet, pole pieces mounted on snifl support in ongegement with the magnet polos, :ly movehle member mounted on snii'l support to Inove between seid pole pieces in response to eurrent through the osoillogreph, und ineens 'for vibrating said support in synohronism .with said member.

9. In un oseillograph, the combination4 with a reflecting gelvanometer comprising; a field magnet, o support pivotaily mounted on the pole of seid muguet, and :i mirror mounted on said support to vibrate about an exis intersecting the exis of the support in resonse to current through the gelvanometer o a synchronous motor connected 'to the source ol seid current to vibrate said support in synehronism with said current.

10. En an oscillograph, lthe combination with :t rollerting gnlvanomete'r comprising n field magnet, n supportpivotully mounted on it pole ot sold. nlngnet, and a mirror mounted on said lsup ort to vibrate about an exis intersecting t ie exis ol the support in response to currentthrough the gnlvenometer, o e synei'nonous. motor connected to the source ot' seiil current, undo. mim on the shaft of snirl motor f'onneetoil to snifl support to vi.- hrute it in synohronism with said current.

1l. `In :in oscillogrnph, the combination with n' reflectingT gnlvanometer having rt mirror mounted to vibrate about two intersectn ing axes, actuating; ineens for rocking.; the mirror on one exis with o synchronously poriodio motion, moons for giving the mirror a motion on the other axis varying with fune-- tion of the energy to he measured, and ineens to prevent the relleotion ot light trein sti-id mirror (turing n `definite port-ion of oooh vibration. 4

12. In :in osoiliograph., the combination with e relier/ting gulvunorneter having n mir ror mounted to wvibrate about two intersecting,r axes, of n, synchronous motor connected to the circuit of the ggilvzinometer, e ouin on the shaft of said motor for vibrating sind mirror, nml n. shutter mounted on the shaft of sind motor to prevent the reitet-,tion of iight 'from said mirror during n predetermined purt of each vibrntion.

ln witness whereof have here-unto my hund this 155th (ley of February, 3.905%.

JOHNTHOH. DifMPS' Et Vi'itnesses BENJAMIN B. HULL, HELEN Gwenn. 

